As the value of oil and gas has continued to rise, there has been increasing interest in methods for effectively retrieving all minerals from known mineral deposits and for discovering new reservoirs. Information about the rate of depletion and the migration of minerals within a mineral reservoir allow operators to apply the most effective production techniques to the particular reservoir conditions. Accurate monitoring of mineral depletion from a given reservoir requires replication of accurate surveys over a long period of time. Also, because differently placed and coupled receivers provide altered results, the seismic receivers need to be placed and coupled similarly for surveys conducted at different times.
One example of an earlier method entails drilling a production borehole, inserting a three-dimensional geophone instrument for data collection, and removing the instrument for mineral production from the borehole. A three-directional geophone is capable of detecting P waves and S waves. This allows for interpretation of: lithography, porosity, pore fluid type, pore shape, depth of burial consolidation, anisotropic changes in pressure, and anisotropic changes in temperature. However, if subsequent readings are to be obtained, production must cease and the instrument must be reinserted into the borehole. The position and coupling of the geophone receiver will not be the same as before and will, therefore, produce skewed data from that initially taken. Thus, even though this method detects both S and P waves, it is difficult to compare subsequent surveys because of different geophone positioning and coupling.
A second example of an earlier method comprises deploying geophones at various locations on the surface and taking readings. Once the survey is completed, the receivers are retrieved for subsequent use at another survey project. In an ocean survey, the water and mud layer typically kill the S waves so that they do not propagate up into the mud or water where they could be received by seismic instruments positioned there. This is also true for the soft earth surface layer of land surveys. Thus, the data collected at the surface is not as accurate as data collected from deep within a borehole. Also, like the previous method, if survey data is to be collected at a later time, the receivers must be re-deployed upon the surface. Again, the receivers are not likely to be positioned and coupled as in the first survey.
Therefore, in order to provide accurate surveys of reservoirs over time, there is a need for repeatability in the location of seismic receivers and in detection of both S-wave and P-wave signals.